cache: Implement RangeOption #1825

backend/cache/object.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/ncw/rclone/fs"
 	"github.com/ncw/rclone/fs/hash"
+	"github.com/ncw/rclone/lib/readers"
 )
 
 // Object is a generic file like object that stores basic information about it
@@ -219,19 +220,21 @@ func (o *Object) Open(options ...fs.OpenOption) (io.ReadCloser, error) {
 
 	var err error
 	cacheReader := NewObjectHandle(o)
+	var offset, limit int64
 	for _, option := range options {
 		switch x := option.(type) {
 		case *fs.SeekOption:
-			_, err = cacheReader.Seek(x.Offset, os.SEEK_SET)
+			offset, limit = x.Offset, 0
 		case *fs.RangeOption:
-			_, err = cacheReader.Seek(x.Start, os.SEEK_SET)
+			offset, limit = x.Decode(o.Size())
 		}
+		_, err = cacheReader.Seek(offset, os.SEEK_SET)
 		if err != nil {
-			return cacheReader, err
+			return nil, err
 		}
 	}
 
-	return cacheReader, nil
+	return readers.NewLimitedReadCloser(cacheReader, limit), nil
 }
 
 // Update will change the object data

lib/readers/limited.go

@@ -0,0 +1,22 @@
+package readers
+
+import "io"
+
+// LimitedReadCloser adds io.Closer to io.LimitedReader.  Create one with NewLimitedReadCloser
+type LimitedReadCloser struct {
+	*io.LimitedReader
+	io.Closer
+}
+
+// NewLimitedReadCloser returns a LimitedReadCloser wrapping rc to
+// limit it to reading limit bytes. If limit == 0 then it does not
+// wrap rc, it just returns it.
+func NewLimitedReadCloser(rc io.ReadCloser, limit int64) (lrc io.ReadCloser) {
+	if limit == 0 {
+		return rc
+	}
+	return &LimitedReadCloser{
+		LimitedReader: &io.LimitedReader{R: rc, N: limit},
+		Closer:        rc,
+	}
+}